What a grinder wheel is
A grinder wheel, or grinding disc, is an abrasive accessory that spins on a grinder to remove, shape, smooth or cut material. The term covers a wide range of products: bonded abrasive wheels made from grains held in a resin bond, flap discs made of overlapping abrasive cloth, wire wheels, diamond wheels and surface-conditioning pads.
Wheels are usually classified by shape, abrasive grain, grit size and bond, and by the job they are designed for. This guide focuses on wheels used on angle grinders, with a note on bench grinder wheels. For the grinders themselves, see types of angle grinders.
Grinder wheel types by shape
Bonded abrasive wheels use standard “Type” numbers, which are widely used in North America. Other regions may use different designations, so check the label.
- Type 1 (straight wheel): a flat disc, commonly used on bench and pedestal grinders. Thin Type 1 wheels are also used for cutting on angle grinders.
- Type 27 (depressed center): has a recessed hub so the mounting nut sits below the wheel face, letting the wheel lie flat against the work. It is the common shape for angle grinder grinding wheels, and is also made as a thin cut-off wheel.
- Type 28 (saucer): a shallow, angled profile intended for corners and contoured areas.
- Type 29 (conical flap disc profile): a common flap disc shape with angled, conical flaps, useful for blending and contouring welds.
- Cup and cylinder wheels: deep profiles used for heavy removal on stone or concrete, often with diamond or abrasive segments.
Common wheel and disc types by job
Grinding wheels. Thick bonded wheels for stock removal, weld grinding and shaping. They are designed to take face pressure, and they remove material quickly but leave a rough finish.
Cut-off wheels. Thin wheels designed for slicing metal or masonry. They are not made for side grinding, because the thin body is not built to take side load. See cutting wheel types for a full guide.
Flap discs. Overlapping abrasive flaps bonded to a backing. They grind and finish in one tool and are popular for blending welds, deburring and smoothing. They tend to leave a better finish than a bonded grinding wheel.
Wire wheels and cups. Wire brushes in wheel or cup form, for removing rust, paint, scale and weld spatter. Wire can break off in use, so eye and face protection is essential.
Diamond wheels and cups. Industrial diamond bonded to a metal or resin body, used for masonry, concrete, tile and stone rather than ordinary steel. Diamond cup wheels are commonly used to grind concrete surfaces.
Polishing and surface-conditioning pads. Non-woven or soft pads for blending, cleaning and finishing. They are gentler and suit jobs where finish matters more than removal speed.
Abrasive grain and grit
The abrasive grain is the material that does the cutting.
- Aluminum oxide: a general-purpose, economical grain for steel and other ferrous metals.
- Zirconia alumina: a tougher grain, often used on flap discs for heavier grinding on steel.
- Ceramic alumina: a premium grain that tends to last longer and run cooler, often chosen for stainless steel and hard alloys.
- Silicon carbide: hard and sharp, often used on non-ferrous metals, stone and some cast iron work.
Grit size is a number indicating particle coarseness. Lower numbers are coarser and remove material faster, and higher numbers are finer and leave a smoother surface. A common approach is to start coarse for removal and move to finer grits for blending and finishing.
Type 1 vs Type 27 grinding wheels
The key difference is geometry. A Type 1 wheel is flat and straight, and is typically mounted on a bench grinder or used as a thin cutting wheel. A Type 27 has a depressed center, so the hub sits back and the wheel face can lie flat on the work. On an angle grinder, Type 27 is the usual choice for grinding. For cutting wheels the same logic applies: Type 1 favors cutting depth, and Type 27 gives clearance for flush cuts.
Choosing a wheel
| Task | Often suitable |
|---|---|
| Heavy weld or stock removal on steel | Type 27 grinding wheel |
| Blending welds and smooth finishing | Flap disc |
| Cutting sheet, tube or bar | Thin cut-off wheel |
| Rust, paint and scale removal | Wire wheel or cup |
| Concrete or stone | Diamond cup wheel or blade |
| Final polishing | Polishing or surface-conditioning pad |
Check the wheel suits the material. For stainless steel, wheels labeled as low in iron, sulfur and chlorine are often recommended to limit contamination.
Fitting and using wheels safely
- Check the wheel’s maximum rated speed and make sure it is at or above the grinder’s no-load speed. Match the diameter and arbor hole to the tool.
- Inspect for cracks, chips or damage before mounting, and never use a dropped or damaged wheel.
- Keep the guard in place and wear eye or face protection, hearing protection and gloves.
- Use the wheel only for its intended purpose. For example, do not side-grind with a cut-off wheel.
- Store wheels dry and flat, away from moisture and damage.
Follow the wheel manufacturer’s instructions and local safety standards.
FAQ
What is a grinding disc used for? Removing material, shaping edges, smoothing welds, and cleaning or preparing surfaces. The type of disc determines how aggressive or fine the result is.
What is the difference between Type 1 and Type 27 grinding wheels? Type 1 is a flat straight wheel, while Type 27 has a depressed center so the wheel can lie flat against the work, as explained above.
What are the different types of side grinders? “Side grinder” is another name for an angle grinder. They are grouped by power source (corded, cordless, air-powered) and disc size, which we cover in types of angle grinders.
What are the three basic types of surface grinders? Surface grinders are precision machine-shop tools, different from handheld grinders. Machining references classify them by spindle and table layout, so consult one for specifics.